The invention relates to a circuit arrangement for monitoring current in a switching converter having an inductance charged in pulse-wise fashion with a current via a power switch.
In switching current supplies, switch-mode converters, and similar circuit arrangements, high currents are periodically connected to inductances via power switches. Here the problem occurs that on the occurrence of an excess current, the current in the power switch, i.e. in the semiconductor switching element, must be limited in order to prevent the destruction of these switching elements. The excess current can be produced by overload, a short-circuit, or by the run-up of switching regulators under a capacitive load.
Fuses and magnetic excess current circuit breakers are generally too slow to protect the semiconductor, i.e. the power switch, in the event of a rapid increase in current. Furthermore, these elements break the circuit in an irreversible manner. For this reason, it is known to connect measuring impedances, i.e. so-called shunts or current transformers, into the circuits which are to be protected, and by means of an appropriate electronics analyis unit, to disconnect the power switch on the occurrence of an excess current therein. These techniques are described in the book "Schaltnetzteile" by J. Wustehube, Chapter 5.41 and 5.42 and 12.10.3. These techniques not only result in great expense, but also result in an undesired voltage drop in the load circuit. Furthermore, special embodiments must be selected for the measuring impedances on account of their low-ohmic characteristics.